Translate text to phone keys

escrevendo-celular-spec.js

var assert = require ('assert'),
  translatePhoneLetters = require('./escrevendo-celular').translatePhoneLetters;

describe('translatePhoneLetters', function() {
  it('chamada vazia', function () {
    assert.equal(translatePhoneLetters(), '')
  })

  it('vazio', function () {
    var str = ''
    assert.equal(translatePhoneLetters(str), '')
  })

  it('A = 2', function () {
    var str = 'A'
    assert.equal(translatePhoneLetters(str), '2')
  })

  it('B = 22', function () {
    var str = 'B'
    assert.equal(translatePhoneLetters(str), '22')
  })

  it('C = 222', function () {
    var str = 'C'
    assert.equal(translatePhoneLetters(str), '222')
  })

  it('D = 3', function () {
    var str = 'D'
    assert.equal(translatePhoneLetters(str), '3')
  })

  it('AD = 23', function () {
    var str = 'AD'
    assert.equal(translatePhoneLetters(str), '23')
  })

  it('AA = 2_2', function () {
    var str = 'AA'
    assert.equal(translatePhoneLetters(str), '2_2')
  })


  it('AB = 2_22', function () {
    var str = 'AB'
    assert.equal(translatePhoneLetters(str), '2_22')
  })

  it('espaço = 0', function () {
    var str = ' '
    assert.equal(translatePhoneLetters(str), '0')
  })

  it('TESTE DO OTAVIKO!!!!', function () {
    var str = 'SEMPRE ACESSO O DOJOPUZZLES'
    assert.equal(translatePhoneLetters(str), '77773367_7773302_222337777_777766606660366656667889999_9999555337777')
  })

})

escrevendo-celular.js

const separator = '_'

const keyboard = [
  ['2', 'ABC'],
  ['3', 'DEF'],
  ['4', 'GHI'],
  ['5', 'JKL'],
  ['6', 'MNO'],
  ['7', 'PQRS'],
  ['8', 'TUV'],
  ['9', 'WXYZ'],
  ['0', ' ']
]

function appendSeparator(letters, letter) {
  return letters.includes(letter) ? separator : ''
}

function getCodeFromLetter (letter, next) {

  const [key, letters] = keyboard.find(keyGroup => keyGroup[1].includes(letter));

  return key.repeat(letters.indexOf(letter) + 1) + appendSeparator(letters, next)

}

function translatePhoneLetters (str) {
  return str && str.length ?
    str.split('').reduce((acc, letter, i, arr) => acc + getCodeFromLetter(letter, arr[i+1]), '') :
    ''
}

exports.translatePhoneLetters = translatePhoneLetters;